(S 1-2s),, 1~2 mm, 35. -, 34~56cm 1.5~2mm 1 1.5, 1 7,, 4~9cm, 3~5cm, 22. -, 5%~10% -,, 1.5~6cm, 34.,, 3~15mm 33.,, 21.,, 1~4 mm, 17~23 mm,

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1 GeologicalScienceandTechnologyInformation Vol.36 No.4 Jul doi: /j.cnki.dzkq ,,. U-Pb [J].,2017,36(4):1-9. U-Pb,,,, (, ) : U-Pb (424.5±6.4)Ma ; : ; ; :P :A : (2017) [8] -, [1] ;, [2-3], -, [4] [5] [9] [1-3], 2 5cm -, U-Pb, -, 1 ( 1) : ( 1) (D 2-3y) 36., 12~110cm, 1~4 mm, 0.5~1 [6], 9~15cm, 135, 12 ~13 [7], 2cm -, 15cm, : : : ( ); - - (DD ) : (1984 ),, - pengli198666@163.com

2 (S 1-2s),, 1~2 mm, 35. -, 34~56cm 1.5~2mm 1 1.5, 1 7,, 4~9cm, 3~5cm, 22. -, 5%~10% -,, 1.5~6cm, 34.,, 3~15mm 33.,, 21.,, 1~4 mm, 17~23 mm, 17~36cm,,, 0.3~1 mm (0.5~2cm), 2~5cm, 5~37cm 32. -, 20., 2~5 2~7cm, cm, 1.5~4cm,, 1~3cm, 14~40cm, 1~4cm,, ( ), 19. -, 15%~20%, 3~6cm, 4~23, 1~3mm, 15cm cm 67~150cm, 31.,,, 2~7mm, 1~3mm, 12~39cm, 3~37mm, ~65cm, 1 5, 10cm, 0.2~1.5mm 1.5~ 30. -, 9cm,, ,, 36cm, 7cm ~5cm, 1~2cm, 10%, ~15cm,,, 13~, 38cm 7~15cm,, 0.5~1 mm, 4~24 mm, 31~66cm, 0.5~2cm,,, 0.7~ , mm, 1~1.2mm,, 15. -, 11~ 2~11cm, 5~21cm,, 30cm 23cm, 54cm 9, 20%,, 27. -, 14. -, 6~34cm, 1~1.2mm, 6~14cm, 23 1,, ,, 4~20cm,,, 1~4 mm, 0.3~0.7 mm, 1.2~3cm,,, ~2mm;, , ~26 cm, 12., 5cm, ~40cm,,, ~3mm,,,, ~2mm , 1 3,, 1 9,, 7~40cm,,, 11.,

3 4 : U-Pb 3 1 Fig.1 LaozhaixiprofilelocationandregionalgeologicalsurveyatEnshi,Hubei 10. -, 3.5~ ~26cm,,, 4cm,,,,, 1~2 mm,, ~2cm 1 1, 9. -, 1 7, 1 2, 1~7cm, 4~ ,, cm 15 1, 1 1,, 0.7~30cm,,, 0.5~1 mm, 1~2mm 5., 1.5 1, , 203cm,

地质科技情报４状细砂岩单层厚度２６４８ｃｍ块状构造细粒结构３黄绿色厚层状粉砂质泥岩夹细砂岩条带或透镜状粉砂质泥岩以平行层理为主页理不发育下部以细砂岩条带为主向上逐渐变２０１７年条带总厚度１７２１ｍ上部以富含生物化石的黄绿色粉砂质泥岩夹粉砂岩生物屑灰岩透镜体为主

状构造细粒结构岩石单层厚度３１３ｃｍ岩石厚度以下部厚层中部薄层上部中层状为特征１灰色巨厚层状细砂岩新鲜面青灰色块状构造单层厚度１４３１４７ｃｍ各层具一定的韵律变化表现为下部细砂岩粒度较粗圆形或不规则状多见具单晶结构的海百合茎少见具网状单晶结构的海胆类两者个体０

成分为黏土矿物少见云母石罗惹坪组Ｓ１ｌｒ０灰绿色中厚层状粉砂质泥岩夹粉砂岩透镜体或条带粉砂岩透英局部可见纹路清晰的层理构造新鲜面蜡状光泽图３镜下观察发现图４岩石成分较简单主要由镜体短轴１３ｃｍ长轴２１１ｃｍ下部少见条带宽１５２６ｃｍ之间总体上下部粉砂质泥岩与粉砂岩的比率为４１

4 地质科技情报４状细砂岩单层厚度２６４８ｃｍ块状构造细粒结构３黄绿色厚层状粉砂质泥岩夹细砂岩条带或透镜状粉砂质泥岩以平行层理为主页理不发育下部以细砂岩条带为主向上逐渐变２０１７年条带总厚度１７２１ｍ上部以富含生物化石的黄绿色粉砂质泥岩夹粉砂岩生物屑灰岩透镜体为主总厚度９４３ｍ少上部以透镜状为主条带或透镜体宽度１３１１ｃｍ平行纹层生物屑灰岩镜下显示图２生物种类以棘皮类间距３５ｍｍ透镜体长轴范围１５２７０ｃｍ该层下部泥砂比为为主次为三叶虫腕足类棘皮类外形呈方形或近２１向上变大为１０１上部粉砂质泥岩由黄绿色变为青灰色２灰色青灰色中薄层状细砂岩细砂岩呈块状构造细粒结构岩石单层厚度３１３ｃｍ岩石厚度以下部厚层中部薄层上部中层状为特征１灰色巨厚层状细砂岩新鲜面青灰色块状构造单层厚度１４３１４７ｃｍ各层具一定的韵律变化表现为下部细砂岩粒度较粗圆形或不规则状多见具单晶结构的海百合茎少见具网状单晶结构的海胆类两者个体０２４３ｍｍ三叶虫外形呈弯钩状具玻纤结构个体０５７２ｍｍ腕足类具平行片状结构个体１４ｍｍ该层斑脱岩出露宽度在５７ｃｍ之间走向上较为连续新鲜色为灰绿色水浸湿后显灰色风化向上粒度变细并含少量泥质成分后呈灰黄色相对较为松散在走向上由于后期压实整合作用呈凹凸状主要成分为黏土矿物少见云母石罗惹坪组Ｓ１ｌｒ０灰绿色中厚层状粉砂质泥岩夹粉砂岩透镜体或条带粉砂岩透英局部可见纹路清晰的层理构造新鲜面蜡状光泽图３镜下观察发现图４岩石成分较简单主要由镜体短轴１３ｃｍ长轴２１１ｃｍ下部少见条带宽１５２６ｃｍ之间总体上下部粉砂质泥岩与粉砂岩的比率为４１向上该比率增大黏土矿物组成主要为显微鳞片状的蒙脱石和水云母含少量隐晶质的高岭石多具黏土化并残余各种凝灰物假象有的呈尖棱角状或不规则外形的晶屑３斑脱岩特征班脱岩产在纱帽组碎屑岩段与含灰岩透镜体段之间下部碎屑岩段总体具有向上粒度变细的特征底部以灰色浅灰色巨厚块状细砂岩为主向上为黄绿色灰黄色粉砂岩泥质粉砂岩夹细砂岩图３斑脱岩露头照片镜头方向ＮＥＦｉｇ３Ｐｉｃｔｕｒｅｏｆｂｅｎｔｏｎｉｔｅａ正交偏光黏土化浅色部分并残余各种凝灰物假象显示残余凝灰结构ｂ正交偏光残余岩屑内大的有呈弧面棱角状的玻屑铁质矿物黑色图２生物屑灰岩镜下特征图４斑脱岩显微照片Ｆｉｇ２ＭｉｃｒｏｓｃｏｐｉｃｆｅａｔｕｒｅｓｏｆｂｉｏｃｌａｓｔｉｃｌｉｍｅｓｔｏｎｅＦｉｇ４Ｍｉｃｒｏｐｈｏｔｏｏｆｂｅｎｔｏｎｉｔｅ

5 4 : U-Pb 5, (CL), ( 5) ( ),,,, (, ) - U-Pb ( ), ( (Agilent7700) 193nm, ) (GeoLasPro), [12- (, ) 14] NIST610, 91500, 4 GJ-1 ICPMSDATACAL9.9 ( 1) 1σ, 91%, SHIRMP U-Pb, [10-11] 5 CL Fig.5 Representativecathodoluminescence(CL)imagesofzircons

6 , Eu,Ce ( 6-a) (424.5±6.4)Ma( 6-b,c, d) 68 U-Pb ( 1) 27 (2014 ),, 41 (428.2~422.9 Ma), 90% Table1 1 U-Pb U-Pbisotopeanalysesforzirconsfrombentonite Th U Th/ t/ma / w B /10-6 U 207 Pb/ 206 Pb 1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ 207 Pb/ 206 Pb1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ % PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM

7 4 : U-Pb 7 1 Th U Th/ t/ma / w B /10-6 U 207 Pb/ 206 Pb 1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ 207 Pb/ 206 Pb1σ 207 Pb/ 235 U 1σ 206 Pb/ 238 U 1σ % PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM PM error error PM PM PM a. ;b. ;c.u-pb ;d. U-Pb Fig.6 6 U-Pb U-Pbconcordiadiagramsforzirconsfrombentonite 6, U-Pb 6.1,,,

8 : 6.2 [R].,2005. [2] [15,5] [5] P.eopennatus, P.a.angularis, ,,,,2010,49(1): [6] [16-17],1925,4(1):39-44.,,1949,29(1/4): m,, [8],, [M]. [9], 29(4): [11],,. [J].,2002,48( ): [18] , U-Pb 480~398 Ma, 456~419 Ma [19-24] 2008,257(1/2):34-43.,, [25-27] Petrology,2010,51(1/2): [15],,,,, [1],, ,1990. :. [M]. : [3]. [M]. :, [4],,.1 5 [R]. : [5],,.Pterospathoduseopennatus( ) [J].. [J]. [7]. [J].,. (2): :, [J].,1990, [10]Su W B,ZhangS H,HufW D,etal.SHRIMP U-Pbagesof K-bentonitebedsintheXiamalingFormation:Implicationsfor revisedsub-divisionofthe Meso-to Neoproterozoichistoryof thenorthchinacraton[j].gondwanares.,2008,14(3):543- SHRIMP mentandrefinementofzirconu-pbisotopeandtraceelement analysesbyla-icp-ms[j].chinesesci.bul.,2010,55(15): MS withoutapplyinganinternalstandard[j].chem.geol., [14]LiuYongsheng,GaoShan,HuZhaochu,etal.Continentaland oceaniccrustrecycling-induced melt-peridotiteinteractionsin thetrans-northchinaorogen:u-pbdating,hfisotopesand traceelementsinzirconsfrom mantlexenoliths[j].journalof,. [J].,1999(4): [16]. [J].,2001,25 500~387 Ma [24], (2): [17],2001,25(1):1-12. [18],, :,2013,43(10): [19] , [J].Geochem.J.,2005,39(6): ,,,LenzA C. [J].. [J].. [J].,2012,31(7): [20]ZhouJC,JiangSY,WangXL.Re-OsisochronageofFankeng basaltsfronfujianofse Chinaanditsgeologicalsignificance [12]Liu Yongsheng,HuZhaochu,ZongKeqing,etal.Reappraise- [13]LiuYongsheng,HuZhaochu,GaoShan,etal.Insituanalysis ofmajorandtraceelementsofanhydrousmineralsbyla-icp- [21]ZhouJC,JiangSY,WangXL,etal.Studyonlithogeochemis- tryofmiddlejurassicbasaltsfromsouthernchinarepresented bythefankengbasaltsfrom YongdingofFujianProvince[J].

9 4 : U-Pb 9 ScienceinChina:EarthSciences,2006,49(10): [22] WangYJ,Fan W M,ZhangG W,etal.Phanerozoictectonics ofthesouthchinablock:keyobservationsandcontroversies [J].GondwanaRes.,2013,23(4): [23] WanYS,LiuD Y,Xu M H,etal.SHRIMP U-Pbzircongeo- chronologyand geochemistry of metavolcanicand metasedi- mentaryrocksinnorthwesternfujian,cathaysiablock,china: Tectonicimplicationsandtheneedtoredefinelithostratigraph- icunits[j].gondwanares.,2007,12(1): [24] WanYS,LiuD Y,WildeS M,etal.EvolutionoftheYunkai terrane,south China:Evidencefrom SHRIMPzircon U-Pb dating,geochemistryand Ndisotope[J].J.AsianEarthSci., 2010,37(2): [25],,,. : [M]. :,2004: [26],. [J].,2003,3(4):2-15. [27],,,. [J].,2009,31(1): DiscoveryofBentoniteinSilurianShamaoFormationin WesternHubei:ImplicationonGeochronologyofU-PbZircon LiPeng,HuZhengxiang,WuLong,DuXiaofeng,Zong Wei,ZhouFeng,MaoQixi (HubeiInstituteofGeologicalSurvey,Wuhan430034,China) Abstract:TherearebigdisputesofthechronostratigraphicdivisionoftheShamaoFormationonthere- searchofyangtzeblockinrecentyears.themainbodyofshamaoformationin western Hubeiiscom- posedofsandandmudstone,butatthetopisformedbytheclasticrockwithbioclasticlimestone.theage ofbentonitefoundintheuppershamaoformationcanrepresentstheageofsedimentation.by meansof theu-pbzircondatingonthisbentonite,weobtainedtheweightmeanage424.5±6.4ma,indicatingthat thesedimentationoccurredinthe Wenlock.Inaddition,ourdatingonthebentonitesuggeststheShamao Formationiscross-timestratigraphicunitandbelongstoEarly-MiddleSilurian.Theoccurrenceofthis bentoniteinthelowersectionofthebiostromallimestonemassorbandindicatesthelimestoneisthestart ofthemiddlesilurian. Keywords:ShamaoFormation;bentonite;geochronology

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